An indexable rotary cutting tool is practically used, in which a cutting insert made of cemented carbide (hereafter, referred to as “cutting insert”) including a cutting edge is detachably attached to an insert mounting seat formed at a tip portion of a cutting tool for a milling using a clamp screw. This indexable rotary cutting tool has a plurality of the cutting inserts attached thereto, and thus can perform a high-efficiency cutting on a workpiece under a high-feed cutting conditions, for example, where a feed per tooth is set to be about 0.8 to 1.0 (mm/tooth) when the workpiece is carbon steel or the like.
However, in the high-feed cutting, a large load of the cutting (cutting force) is applied to the cutting insert, and thus there are some trouble where early wear of the rake face and the flank face of the cutting edge and chipping and fracture of cutting edge of the cutting insert occur, and thus quality of the machined surface is deteriorated and the tool life of the cutting insert is shortened.
Regarding the indexable rotary cutting tool to which the cutting insert is detachably attached to the insert mounting seat thereof, in order to improve the above-mentioned troubles, there are some proposals in the related art.
For example, an improvement for improving a chip disposability while retaining the stiffness of the cutting insert main body and the installation rigidity of the cutting insert by forming a concave-groove breaker on a rake face of a cutting insert (PTL 1); an improvement for increasing the strength of the tip portion of the tool by improving a shape, arrangement and the like of the cutting edge provided on the cutting insert (PTL 2); and an improvement for allowing the cutting insert to be stably attached to the insert mounting seat even in small indexable rotary cutting tool by contriving the shapes of the cutting insert and the cutting edge so as to provide the cutting insert with a sufficient size of a mounting face (PTL 3), are suggested.
The configurations of the above-mentioned improvements suggested in PTLs 1 to 3 are further described as follows.
PTL 1 (Japanese Unexamined Patent Application, First Publication No. 2003-275920) suggests an invention of a cutting insert (indexable insert) which is capable of machining a horizontal plane and a vertical wall with respect to a machined surface of a workpiece and in which the number of usable cutting edges in one cutting insert is increased.
In the cutting insert suggested in PTL 1, the cutting insert (insert main body) formed into a polygonal plate shape has: a top surface and a bottom surface (top and bottom surfaces) formed into a polygon as a rake face; a corner edge formed into a circular arc and formed at a corner portion shared with the top surface and the bottom surface; and a major cutting edge formed at a ridgeline portion of the top and bottom surfaces continuous to one end portion of the corner edge. On the other hand, a ridgeline portion of the top and bottom surfaces continuous to the other end portion of the corner edge is formed symmetrically with the major cutting edge about the bisector of the circular arc formed by the corner edge. Between the top and bottom surfaces of the cutting insert main body, the corner edge, the major cutting edge, and the ridgeline portion continuous to the other end portion of the corer edge of each of the top and bottom surfaces are arranged so as to be symmetrical with each other when the top and the bottom surfaces of the cutting insert main body are reversed.
In FIG. 11 of PTL 1, a configuration is suggested, in which a concave-groove breaker is formed on the top and bottom surfaces along the major cutting edge from the corner edge so as to avoid a periphery of the ridgeline portion at least near the corner edge. PTL 1 describes that this concave-groove breaker is provided in order to improve the chip disposability and surely retain the stiffness of the insert main body and the installation rigidity of the insert.
PTL 2 (Japanese Patent No. 5007853) suggests a cutting insert and an indexable cutting tool which can increase the strength of the tip portion of the tool.
The cutting insert disclosed in PTL 2 is a cutting insert including: two end surfaces having a main face which can be used as an attachment face to a tool main body; a periphery side surface extending between the two end surfaces; and a plurality of cutting edge portions formed at intersecting portion where the periphery side surface intersects with each of the end surfaces. A plurality of the cutting edge portions are arranged so as to have rotational symmetry around the first axis passing through the two end surfaces and have rotational symmetry around the second axis orthogonal to the first axis and passing through the periphery side surface. An intermediate plane orthogonal to the first axis and containing the second axis and passing through the periphery side surface is defined.
In the cutting insert disclosed in PTL 2, each of the cutting edge portion includes: a corner edge formed at a corner portion of corresponding end surface; a major cutting edge extending from one end of the corner edge so as to have a distance between the major cutting edge and the intermediate plane which is longer than a distance between the intermediate plane and the main face of the corresponding end surface; and a minor cutting edge extending from the other end of the corner edge so as to have a distance between the minor cutting edge and the intermediate plane which is longer than a distance between the intermediate plane and the main face of the corresponding end surface. PLT 2 describes that a concaved chip breaker is provided between each cutting edge and the main face of the end surface.
PTL 3 (Published Japanese Translation No. 2011-516292 of the PCT International Publication) discloses a cutting insert including: an upper surface and a lower surface positioned at opposite side to each other; and two longitudinal side surfaces and two transverse side surfaces connecting the upper surface and the lower surface, of which the length in the longitudinal direction is longer than that in the transverse direction. A penetrating hole penetrates through the center portions of the upper surface and the lower surface. The two longitudinal side surfaces are positioned at opposite side to each other and are perpendicular to the upper surface and the lower surface. The two transverse side surfaces are positioned at opposite side to each other and are perpendicular to the upper surface and the lower surface. On the upper surface and the lower surface, corner edges are provided at corners on one diagonal and chip discharge flutes are provided at corners on the other diagonal. A chip discharge flute extending along the transverse side surface is formed on each of the upper surface and the lower surface.
The chip discharge flute disclosed in PTL 3 includes: a chip discharge flute tilting downwardly toward one longitudinal side surface with respect to the longitudinal axis S2; and a chip discharge flute tilting upwardly toward the other longitudinal side surface.
On each of the upper surface and the lower surface, the corner cutting edges are formed at a pair of the corners on one diagonal among the four corners, and the two corners on which the corner cutting edges are formed protrude above the other corners on the upper surface or the lower surface.